Why Is My Swimming Pool Green?

(1) No chlorine exists in the water. Without chlorine present, algae thrives and leads to an "algae bloom". It will be necessary to add more than the usual amount of chlorine to shock it back to ideal conditions. In addition, it is recommended that you run your filter pump 24/7 until pool water is returned to ideal conditions. After heavily shocking (adding granular chlorine) to your pool, it may cloud briefly, but you should begin to see the green changing to blue. The additional filtration time will take care of any cloudiness usually.

You should also check the pH and the Total Alkalinity. An imbalance in these two factors, especially if they are too low, will create an ideal environment for algae growth. Ideal level, in a gunite pool, for pH, is 7.4. A range of 7.2-7.6 is acceptable. For the Total Alkalinity, in a gunite pool, it is recommended you maintain it between 80-120 ppm.

(2) Filter time may not be sufficient. Especially during a hot Texas summer, it is recommended to run your filter pump a minimum of 8 hours daily, perhaps as much as 10-12 hours in cases of heavy bather load. Even during the winter, filter pump should be run a minimum 8 hours daily. Many experts claim that 4-6 hours is enough time for all the water in an average residential pool to be filtered once, but heavy use and high temperatures dictate running the pump more.

(3) Filter may be compromised. If it hasn't been backwashed and/or cleaned recently, the circulation may be rather poor. In the case of a Diatomaceous Earth filter, grids or manifold may be damaged, allowing the filter media to return to the pool. In a sand filter, sand may be old and packed down, and not stirring around while being backwashed. Cartridges may have reached their capacity and need to be cleaned or replaced.

(4) In some cases, the cyanuric acid level is so high that it makes it difficult to maintain balanced water. Total dissolved solids (TDS) can also cause balancing problems. In both cases, it will be necessary to drain much of the water from pool and replace it. Don't forget to balance the water afterwards. Following these steps will help keep your pool looking beautiful all season.